Grease an 8-inch baking round and line it with a circle of parchment paper.
In a large bowl, using a handheld mixer or stand mixer, cream the ¾ cup unsalted butter and 1 cup light or dark brown sugar together on medium speed until light and fluffy, about 3 minutes. Beat in the 2 eggs and 2 teaspoons pure vanilla extract on medium-high speed until combined. Scrape down the sides and bottom of the bowl as needed.
In a separate bowl, whisk together the 2 cups whole wheat flour, 1 teaspoon baking soda, and ½ teaspoon fine sea salt. Beat the dry ingredients into the wet ingredients on low speed until combined. Fold in the 1 ½ cups semi-sweet chocolate chips.
Press the batter evenly into the prepared pan and let it rest for 20 minutes. The batter will be thick. Then, preheat the oven to 350°F and bake for about 25-30 minutes until the surface of the cake is golden brown and a tester comes out mostly clean.
Transfer the pan to a wire rack to cool completely. Place the cake on a plate and cut wedges to serve, or cut and serve it directly from the pan.
Notes
What size pan? For a thicker cookie cake, use an 8-inch cake pan. For a thinner cake, bake the batter in a 9-inch round.
Batter will be thick. This is a thick cake batter, and especially so because of using whole grain flour, which absorbs more liquid.
Use room temperature ingredients. As with baking cookies, starting with room temperature/softened butter will create a smooth and fluffy base for the rest of the ingredients. I let my butter sit out on the counter for an hour, or warm it quickly in the microwave for 15-20 seconds.
Try all-purpose flour. If needed, swap all-purpose flour for the whole wheat flour. I also like to use spelt flour, another whole grain flour choice.
Coconut sugar for the brown sugar. For a less sweet/naturally sweet option, use coconut sugar for the brown sugar.